1. Field of the Invention
This invention relates to image forming apparatus for forming images electrophotographically such as copying machines and to an initialization control method for turning function devices included in such an image forming apparatus into their respective predetermined operable conditions after energization thereof.
2. Description of the Related Art
A certain length of time is required for function devices included in an electrophotographic image forming apparatus such as a fixing unit, light-source lamp unit and laser scanning unit to reach their respective operable conditions from the starting of energization thereof. The fixing unit, which functions to fuse a toner image and pressure-bond the fused toner image to a recording medium by heating and pressurizing the recording medium after a transfer step, needs to be heated to a predetermined temperature that allows the toner image to be fused from the starting of image forming processing. The light-source lamp unit, which functions to emit light for reading image information from an original document placed on a platen, needs to emit a predetermined quantity of light for obtaining image data of a proper density from the starting of image reading processing. The laser scanning unit, which functions to scan the surface of a photosensitive member with laser light modulated according to image data, has a polygon mirror for scanning with laser light in a primary scanning direction, which polygon mirror needs to rotate at a predetermined speed from the starting of the image forming processing.
Thus, such an electrophotographic image forming apparatus waits for the function devices of the apparatus to turn into their respective predetermined operable conditions (inclusive of the aforementioned predetermined temperature, predetermined light quantity and predetermined speed) after the starting of energization of the function devices and then starts the image reading processing and the image forming processing. When the units included in the apparatus turn into their respective predetermined operable conditions after the image forming apparatus has been powdered on or re-powered on following settlement of jam or the like, a ready lamp in a display section of the apparatus is turned on to notify the user that the image forming apparatus becomes ready for use.
Heretofore, the time required for the function devices of an image forming apparatus to turn into their respective predetermined operable conditions from the powering-on of the apparatus has been determined by the time required for the fixing unit to reach the predetermined temperature. The time required for the fixing unit to reach the predetermined temperature is what is called “warm-up time”. During the warm-up time of the image forming apparatus, preparations for the starting of image reading processing and image forming processing are made including operations such as to check and adjust the thickness of toner and to initialize the processing parts including the photosensitive member, .while the light-source lamp unit and the polygon mirror of the laser scanning unit are caused to reach the predetermined light quantity and the predetermined rotational speed, respectively. Controls exercised to effect these operations constitute initialization control of the image forming apparatus.
With the development of power-saving image forming apparatus proceeding in these years, the number of apparatus that require a few minutes' warm-up time like conventional apparatus is decreasing, while on the other hand the development of image forming apparatus of the immediate printing type which is capable of starting the image forming operation at substantially the same time with power-on is proceeding. In such an immediate printing type image forming apparatus, the efficiency in raising the temperature of a fusing roller (heating roller) included in the fixing unit by means of a heat source is improved by rendering the fusing roller thinner or by like means, thereby shortening the warm-up time. However, the following problems arise with such immediate printing type image forming apparatus if the warm-up time is determined only by the time required to raise the temperature of the fixing unit up to the predetermined temperature.
That is, as the case may be, a relatively long time is needed not only to raise the temperature of the fixing unit up to the predetermined temperature but also to turn other function devices such as the light-source lamp unit and laser scanning unit into their respective predetermined operable conditions during the warm-up time of the image forming apparatus. This is because the quantity of light emitted from a cold cathode tube that is used as the light-source lamp unit for power saving depends on the bulb temperature of the cold cathode tube and, hence, a prolonged time is required for the cold cathode tube to reach the predetermined light quantity, and because the rotational speed of the polygon mirror included in the laser scanning unit is rising with rising resolution and, hence, a sufficient acceleration time is required to raise the rotational speed of the motor driving the polygon mirror sufficiently.
For this reason, if the warm-up terminates in a short time from power-on at the time when the fixing unit reaches the predetermined temperature, the ready lamp in the display section is turned on even though other function devices of the apparatus than the fixing unit are not ready to operate and, hence, it is possible for the apparatus to accept an instruction from the user to start image reading processing and image forming processing despite the apparatus not in a ready-to-operate state as a whole.
If the image reading processing and image forming processing are executed with the apparatus not in the ready-to-operate state, troubles occur in the image reading processing and image forming processing such that images on an original document are not read normally due to an insufficient quantity of light emitted from the light-source lamp unit and that such images are written inaccurately on the photosensitive member due to the polygon mirror of the laser scanning unit rotating at an insufficient rotational speed. Thus, proper image formation becomes impossible.
In attempt to overcome the foregoing problem, a prior-art image forming apparatus disclosed in Japan Patent Laid Open sho No. 62-6277 is configured to terminate the warm-up after .detection is made of both of the two facts that: the temperature of the fixing unit has reached a predetermined temperature that allows a toner image to fuse; and the light quantity of the light-source lamp unit has reached a predetermined light quantity that allows images on an original document to be read accurately. Also, there have been proposed a number of configurations to terminate the warm-up after the satisfaction is made of both of the two conditions that: the temperature of the fixing unit has reached a predetermined temperature that allows a toner image to fuse; and the rotational speed of the polygon mirror in the laser scanning unit has reached a predetermined speed that allows images to be accurately written on the photosensitive member with laser light.
However, with such prior-art configurations to terminate the warm-up at the time when both of the temperature of the fixing unit and the light quantity of the light-source lamp unit have reached the predetermined temperature and the predetermined light quantity, respectively, or when both of the temperature of the fixing unit and the rotational speed of the polygon mirror in the laser scanning unit have reached the predetermined temperature and the predetermined speed, respectively, the warm-up time cannot be shortened sufficiently, but the warm-up is merely terminated upon elapse of the time required for the temperature of the fixing unit to reach the predetermined temperature, the time required for the light quantity of the light-source lamp unit to reach the predetermined light quantity, or the time required for the rotational speed of the polygon mirror in the laser scanning unit to reach the predetermined speed, whichever the longest. This does not lead to the realization of an immediate printing type image forming apparatus.